Could you please try the same using PI OPC HDA tool for connecting to OPC HDA server. As per the screen shot you are trying to connect to OPC DA and in general server.1 will be enabled for remote access. Request you to check eventvwr for any specific errors. OPC DA/HDA errors are logged in application/system in eventvwr. Identity the class or app ID which is causing issue while connecting. IF you are not sure of the application based on app ID, You can try searching with APP ID in registry using regedit.

DCOM errors are common for applications on different machines and since everything is on the same node it is a bit harder to tell what to check.

Are you running the OPC Client as the OPC User (not sure if it is the 800xa user in this case)?

If for some reason it the client and the server applications are communicating through the network firewall may also be configured. NAT also can be a problem in this case since DCOM does not support it.

I suggest you to call techsupport and go through a remote session in order to narrow down the possible causes.

Have tried to run the OPC Client botha as my self and as the user that will be running the PI OPCHDA interface, both admins on the machine. Don't have the credentials to the user that runs ABB 800xa, but I know that it has been set up on other nodes on this site with different users, though not by me...

The 8ABB0012 is a vendor specific error, in this case ABB. I would suggest taking a look at the logs on the OPC Server and contacting ABB to get the meaning of the error.

In your post, you mention wanting to connect with OPC HDA server, but in the screenshot you are using an OPC DA client and trying to connect with an OPC DA Server. Are you trying to connect to the DA or HDA server?

Could you please try the same using PI OPC HDA tool for connecting to OPC HDA server. As per the screen shot you are trying to connect to OPC DA and in general server.1 will be enabled for remote access. Request you to check eventvwr for any specific errors. OPC DA/HDA errors are logged in application/system in eventvwr. Identity the class or app ID which is causing issue while connecting. IF you are not sure of the application based on app ID, You can try searching with APP ID in registry using regedit.